Our long-term objectives are to examine the clinical roles of tuftsin, a naturally-occurring immunomdulating hormone-like peptide, as an antitumor, anti-microbial and immuno-augmenting agent and also to elucidate the mechanism of action of this peptide. Based on our studies the following specific aims are proposed: 1. Examine growth factor activity of tuftsin in vitro. 2. Examine specific binding of tuftsin to various cells using fluorescein-labeled tuftsin and 3H--tuftsin in vitro. 3. Purify and characterize tuftsin receptors (including tuftsin binding). 4. Conduct biochemical study of fate of tuftsin internalized by granulocytes and monocytes. Tuftsin and its anologs will chemically synthesized and purified in this laboratory.